Coquelin has established himself as a key component for Arsenal's midfield over the last 18 months and the Frenchman has been vital to the Gunners' promising start to the 2015/16 season.
Redknapp wrote in his column for the Daily Mail: "Another 3-0 win for Arsenal and they are right in this title race.
"They've made a much better start than last season and if they finish this campaign as strongly then they have a fantastic chance.
"But the January transfer window is going to be key. Of course they'd love to sign somebody like Karim Benzema but that's not going to happen, especially if Arsenal go out of the Champions League. But there's money in the bank and they should look to reinforce.
"There's plenty of quality but if someone like Francis Coquelin gets injured, is there enough cover? They must be decisive because this is a real opportunity."